1. Field
The invention is in the field of electrode devices for use in the iontophoretic transporting of drug molecules through the skin.
2. State of the Art
The use of iontophoresis to transport a drug in solution through intact skin is well known. It is based on the principle that ions in solution will migrate in the presence of an electrical potential. Iontophoresis is performed by placing an electrode containing an ionic drug source onto the skin through which the drug is to be transported. A second electrode is placed on the skin near the first electrode and voltage is applied sufficient to cause current to pass through the skin between the electrodes. The ionic drug molecules migrate toward the second electrode and are thus transported through intact skin. A particular use of this technique is in the administration of pilocarpine nitrate or chloride to stimulate sweat gland secretion in a localized area of the skin.
In the past, electrode devices used as a drug source in iontophoretic applications have included a drug-soaked pad made of gauze, layers of filter paper, or some other absorbent fabric material. Drug-soaked pads are disadvantageous, however, because pressure on the pad, such as occurs during electrode attachment, forces drug solution out of the pad. Moreover, drug-soaked pads are prone to evaporation. Either of these occurrences leads to an insufficient amount of drug solution in the pad, which exposes the patient to the danger of electrical burns and also makes the amount of drug actually transported through the skin unpredictable. In an attempt to provide a sufficient source of drug ions and to protect against burns, it has been necessary to periodically add drug solution to the drug-soaked pad; but if too much drug solution is added, excess solution may spill onto the skin where it offers a low-resistance path for current to flow across the skin surface, thereby reducing the amount of drug transported through the skin.
Improved versions of the above are shown in Jacobsen et al. U.S. Pat. Nos. 4,141,359 and 4,166,457, and a prefilled disposable unit is shown in Reeves U.S. Pat. No. 3,677,268.
An application of iontophoresis in dentistry is disclosed in U.S. Pat. No. 3,215,139 to V. H. Dietz, who employs sodium alginate as a gel substrate for fluoride ions to be iontophoretically applied to a patient's teeth. Sodium alginate is soluble in water. It and the fluoride are mixed with water to form a sticky, impressionable composition which is allowed to gel around the teeth following application by means of the patient biting into an open receptacle containing the composition. Gelation takes about two or three minutes and the "gel" formed is a heterogeneous, gummy substance, rather than a solid, clear, homogeneous gel. Dietz suggests that other vegetable gums such as gum tragacanth or agar-agar might possibly be substituted for the sodium alginate, although he notes that agar-agar is not very desirable because of the heat involved in its use. Actually, agar-agar, also spoken of merely as agar, is not soluble in water except at elevated temperatures. It could not be satisfactorily employed in the manner disclosed by Dietz.
U.S. Pat. No. 3,989,050 teaches the use of various gels of a mayonnaise-like consistency as conducting materials for application to metallic plate electrodes used for long-time monitoring purposes. It does not indicate whether or not these gels can be used in iontophoretic applications.
Agar has long been used to prepare solid media for culturing microorganisms. When mixed with the nutrient broth at the common rate of 1.5 to 2.0% (w/v), the agar forms a fibrous structure which is fine enough to prevent motility of bacteria within it but coarse enough to permit diffusion of nutrients.